Known face tracking applications for digital image acquisition devices include methods of marking human faces in a series of images such as a video stream or a camera preview. Face tracking can be used to indicate to a photographer the locations of faces in an image or to allow post processing of the images based on knowledge of the locations of the faces. Also, face tracker applications can be used in adaptive adjustment of acquisition parameters of an image, such as, focus, exposure and white balance, based on face information in order to produce improved the quality of acquired images.
A well-known method of fast-face detection is disclosed in US 2002/0102024, hereinafter Viola-Jones. In Viola-Jones, a chain (cascade) of 32 classifiers based on rectangular (and increasingly refined) Haar features are used with an integral image, derived from an acquired image, by applying the classifiers to a sub-window within the integral image. For a complete analysis of an acquired image, this sub-window is shifted incrementally across the integral image until the entire image has been covered.
A number of variants of the original Viola-Jones algorithm are known in the literature, such as disclosed in U.S. patent application Ser. No. 11/464,083 (FN143). However, such face detection applications are computationally expensive.
It is an object of the present invention to provide an alternative and computationally efficient method of face detection in mid-shot digital images.